The present invention relates to an information recording medium of an air-sandwich sealed type which comprises a pair of disk-shaped substrates to form an inner space therebetween, a pair of inner and outer circumferential spacers interposed therebetween, and a recording layer deposited on the inner surface of at least one of the substrates.
A conventional information recording medium of an air-sandwich type comprises a pair of disk-shaped substrates made of a transparent rigid plate of a resin such as acrylic resin and polycarbonate resin, at least one of which carries on an inner side thereof a recording layer made of a thin metal layer of Te or the like, or an organic pigment layer of phthalocyanine or the like; an inner circumferential spacer 3a shown in FIGS. 3 or 3b shown in FIG. 4 and an outer circumferential spacer interposed therebetween, the inner circumferential spacer being placed at the central portion of the substrates and the outer circumferential spacer being placed at the outer circumference of the substrates. These members are sealed by an adhesive agent, whereby a sealed type recording medium is fabricated. When sticking the spacers to the substrates, the adhesive agent is applied to the spacer surfaces in the form of an adhesive layer 7b as shown by the hatching in FIG. 4. The thus fabricated recording medium is airtight, so that the disk-shaped substrates tend to be deformed to cause the inclination of the surface of the recording layer when there is a difference between the inner pressure of the recording disk and the atmospheric pressure. This readily occurs. Once such surface inclination takes place in the substrates, tracking distortion is brought about when reproducing recorded information from the recording medium.
In order to overcome such a drawback, it has been proposed to provide a vent in the disk-shaped substrates. However, such a vent makes the sealed type recording disk non-airtight, so that the recording layer formed on the inner surfaces of the recording disk readily deteriorates when directly exposed to some adverse materials contained in the air.
Recently, an attempt has been made that when an inner circumferential spacer is struck to a pair of the substrates by an adhesive agent applied in the form of an adhesive layer 7a, a portion to which no adhesive agent is applied is provided as indicated by reference numeral 9a in FIG. 3, which is hereinafter referred to as the cut-away portion. A small gap formed between the substrate and the spacer in the cut-away portion 9a serves as an air passage. However, the thus formed air passage has a length L, at maximum, equal to the width of the inner circumferential spacer as shown in FIG. 3. This length, however, is not sufficient for preventing the recording layer from being directly exposed to the air, so that it is inevitable that the recording layer is deteriorated by the adverse materials contained in the air.
Further, it is extremely difficult to properly adjust the width W of the cut-away portion 9a in actual production in such a manner that the flow rate of the air which may enter the inner space of the recording medium is controlled so as to avoid the above-mentioned problem as long as the length L of the air passage is limited as mentioned above.